Appliances including televisions, refrigerators and so on are operated with external commercial AC (Alternating Current) power. Electronic apparatuses including laptop computers, mobile terminals, PDAs (Personal Digital Assistants) and so on are also operated with commercial AC power and their internal batteries may be charged with the commercial AC power. Such appliances and electronic apparatuses (hereinafter collectively referred to electronic apparatuses) may contain a power supply (inverter) for converting commercial AC power into DC (Direct Current) power. Otherwise, an inverter may be incorporated in an external power adapter (AC adapter) of the electronic apparatuses.